A first technique is known in which, in a network device (for example, a network switch) that performs communication (relaying frames) at the data link layer (layer 2) of the open systems interconnection (OSI) basic reference model over a communication network, the discard reason is displayed for the discarded frame and the discarded frame is output on a different port.
A second technique is also known in which a flag is provided to a processing result of a specific frame that is to be traced, only the processing result to which the flag is appended is stored in memory, and, when the specific frame is normally transferred or discarded, the processing result is output on a different port.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2007-13990 and Japanese Laid-open Patent Publication No. 2008-136081.
In a communication network including a transmission path that couples network switches, when data transmitted from a terminal or the like does not arrive at another terminal or the like which serves as the destination, it is important to know which portion of the network the target data has arrived at, for the purpose of cause analysis and recovery at the time of failure occurrence.
In this regard, with the first technique, although occurrence of discarded frames and reasons for discarding the frames may be identified, in order to determine the association of the discarded frames with the target data, the whole packets contained in all of the discarded frames have to be saved (packet capture) and be analyzed later. Particularly in the case where a communication network includes a large number of network switches, performing a packet capture in each individual network switch results in an enormous storage capacity being used for capturing and also results in imposing a significant analyzing load. This technique is therefore not practical.
With the second technique, the number of discarded frames to be analyzed may be narrowed down based on the count or the like of specific statistical information and error information. However, there is no difference in that, in order to determine whether or not the discarded frames are related to the data in question, packet capture and analysis have to be performed. The problems described above are not solved.